Design and hot embossing of glass micro gratings for polarization-insensitive beam splitter

Abstract

Polarization-insensitive beam splitters play significant roles in the manipulation of optical beams and signal processing. However, existing fabrication methods for glass beam splitters suffer from cumbersome steps, long cycle time, and insufficient accuracy on the micrometer scale. Therefore, it is non-trivial to seek for an alternative method for fabrication of the beam splitters with high efficiency and high precision. This study aims to design a high-performance polarization-insensitive glass beam splitting grating and to demonstrate the efficiency and accuracy of hot embossing technology in its fabrication for the first time. Firstly, the Fourier modal method is adopted to simulate the diffraction efficiency of the beam-splitting gratings with different geometric parameters at the operating wavelength of 808 nm. The effects of different geometric parameters on the diffraction efficiency are evaluated. After that, the optimal geometric parameters of the grating are calculated, with a ridge width of about 6 μm. According to the optimized optical design, the monocrystalline silicon grating is produced by the standard photolithography-etching steps. In the next step, a protective coating is deposited on the silicon mold by the physical vapor deposition. Subsequently, the micro grating features are replicated from the coated silicon mold to the glass substrate by hot embossing. The surface topography of the coated silicon mold and the embossed glass grating are measured by the white light interferometer, showing a decent filling rate of 96.79 %. Moreover, the diffraction efficiency of the glass grating is detected by a home-made optical testing platform, and the detected data are consistent with the simulated ones. Therefore, hot embossing is a promising method for mass production of glass beam splitting gratings.